During cultivation of cells in bioreactors, air and/or other gases are continuously supplied to the reactor and the excess, together with gaseous metabolites from the cells, is removed via an exhaust port. To ensure sterility of the culture, the exhaust line is equipped with a sterilisation grade filter, where the filter medium can typically be a 0.1-0.2 micron hydrophobic microfiltration membrane. Since the exhaust gas stream is warm and saturated with moisture, there is a significant risk that the moisture condenses on the filter medium, causing a blockage of the gas flow through the filter.
Several solutions have been described where a water-cooled condenser is placed in the exhaust line before the filter (U.S. Pat. No. 5,443,985; U.S. Pat. No. 6,133,021; U.S. Pat. No. 7,425,441) or integrated in the filter housing before the filter medium (US 2011/0076759). Any moisture is then condensed and the condensate can flow back to the bioreactor by gravity flow and thus avoiding any contact between liquid condensate and the filter medium. The use of a water-cooled condenser is however complicated in that water must be supplied via tubing, which must be thoroughly secured to the condenser and to a drain in order to avoid any leakage. Further, water-cooled condensers are complicated to manufacture in that double-walled vessels or vessels with internal tubing and tubing ports through the walls are needed. This is a drawback in particular for small to medium scale cell cultivation in disposable bioreactors, where it is highly desirable to use low cost disposable plastic components.
Hence, there is a need for a gas exhaust filter device which can be used in bioreactors without any liquid-cooled condensers.